276 THE EVOLUTION OF THE METAZOA 



type can actually be able to live. I cannot see any likelihood that 

 the supposition that either a planuloid (a "planaea," corres- 

 ponding to a planula of Cnidaria) or a gastruloid animal (a 

 gastraea, corresponding to a gastrula of numerous animal 

 types) had ever existed, is correct. I therefore do not take into 

 consideration such ancestral forms. 



As long as we believe that the Eumetazoa had evolved ex- 

 clusively as a formation of cormi on the pattern of the early 

 stages of the animal ontogeny, which usually takes place by 

 means of a complete cleavage of the fertilized egg cell, we will 

 hardly be able to find any other solution than to accept the 

 existence of a planuloid form or of a modification of the same. 

 Yet if we succeed in freeing ourselves of this truly fascinating 

 idea we find new possibilities, new probabilities emerging 

 before us. Some older zoologists have already thought along 

 the same lines (Dobell, 1911, and before him Saville Kent, 

 Sedgwick, etc.). 



Some zoologists have already called our attention to the 

 extraordinary similarity that exists between the structure of 

 a holotrichous infusorian and of a turbellarian (Fig. 47), at 

 the same time they had no intention of making phylogenetic 

 conclusions on this basis, even if such conclusions have 

 seemed to be tangibly close. We will mention here the detailed 

 comparison only between the Infusoria and the Turbellaria 

 which was made by the well-known Hungarian zoologist V. 

 •Gelei, an expert in Infusoria, in Hydra, and in Turbellaria. In 

 this comparison a whole list of striking similarities has come 

 to light which can naturally also be considered as pure parallel- 

 isms or as accidental similarities. V. Gelei did not think here of 

 possible homologies because there are also differences between 

 these two animal types that can above all be observed in the 

 extremely specialized nuclear apparatus and in the sexual 

 phase of the Infusoria. 



Let us mention here briefly these similarities: (1) the range 

 of the body size; (2) the general form of the body (habitus); 

 (3) the general ciliation of the body surface and the type of 



